1. Field of the Invention
The present invention is directed to an automatic transmission, especially for a motor vehicle.
2. Discussion of the Prior Art
Modem developments in automotive engineering have increasingly moved away from manual shift transmissions, i.e., transmissions in which a shifting force is transmitted mechanically from a gear lever to the transmission, toward automatic transmissions. In these transmissions, the shifting selected by the driver is determined in that a movement of the shift lever is detected by an associated sensor arrangement or automated program and, based on the detected shifting selection, an actuator arrangement is put into operation in the transmission for carrying out the desired shifting procedure. For this purpose, transmissions constructed for manual operation are outfitted in such a way that, e.g., a shifting shaft which is to be moved linearly and possibly rotationally for carrying out a shifting process is moved by means of these actuators which initiate required movements. Accordingly, when carrying out shifting processes, appropriate actuation of the shifting shaft deactivates a coupling device, e.g., in the form of a synchronizing mechanism, adjusting a previously engaged gear and, only after this device has been deactivated by the movement of the shifting shaft, the coupling device associated with the next gear speed to be adjusted is activated in the course of further movement of the shifting shaft. The time required for carrying out a shifting procedure in this way is relatively lengthy because a previously adjusted gear speed must first be fully disengaged and the shifting shaft must then be moved further to the next required position before a new gear speed can be engaged. Another problem consists in that the design of the actuators driving the shifting shaft must be appropriate to the actuating path to be traversed as well as to the required shifting force, so that relatively large drive units are required in order that the necessary shifting force can still be provided in the case of relatively long shifting paths.
Accordingly, it is an object of the present invention to provide an automatic transmission which minimizes the time required for carrying out shifting procedures in a simplified construction.
According to the invention, this object is met by an automatic transmission, especially for a motor vehicle, comprising a plurality of torque transmission paths which can be selectively activated for torque transmission, wherein the torque transmission paths have different transmission characteristics and, based on their transmission characteristics, can be ordered in a sequence of torque transmission paths. The transmission further comprises a clutch arrangement by which at least one of the torque transmission paths can be activated.
It is further provided in the transmission according to the invention that the clutch arrangement has a clutch unit which is associated with a group of torque transmission paths and by which a torque transmission path of a group of torque transmission paths may be selectively activated. A plurality of groups of torque transmission paths are provided, each group comprising only one individual torque transmission path, or a plurality of groups of torque transmission paths are provided, at least one group comprising a plurality of torque transmission paths, or a plurality of groups of torque transmission paths are provided, at least one group comprising an individual torque transmission path and at least one additional group comprising a plurality of torque transmission paths. At least one group of torque transmission paths, insofar as it comprises a plurality of torque transmission paths, comprises only torque transmission paths which do not immediately follow one another in sequence.
As a result of the construction, according to the invention, of an automatic transmission, it is ensured due to the appropriate grouping of different torque transmission paths and the allocation of the same to a respective coupling unit that independence from the predetermined sequence is maintained to a great extent. It is assumed, for instance, that the sequence in which the individual torque transmission paths can be ordered or listed with respect to their transmission characteristics is an indication of the descending speed reduction ratio. Accordingly, this results in a sequence which, in conventional transmissions, is defined by the individual gear speeds: first gear, second gear, third gear, fourth gear, and so on. Since it is now ensured in the transmission according to the invention that two torque transmission paths immediately following one another in this sequence are not serviced by the same clutch unit, it is possible, for example, when carrying out a shifting process from first gear to second gear, to disengage the clutch unit associated with the first gear and to engage the clutch unit associated with the second gear virtually simultaneously or with a slight delay in time, wherein, in this case, the first gear and the second gear are arranged in different groups and therefore are to be activated by means of different clutch units. Accordingly, it is not necessary to wait until the first gear is fully disengaged before activating or engaging the second gear. In this way, an appreciably faster shifting process can be carried out and the inconvenience resulting in the prior art from a period of interruption of tractive force can be appreciably reduced when carrying out the shifting process.
According to the present invention, different alternatives are possible with respect to the grouping of the individual torque transmission paths. Within the meaning of the present invention, the term xe2x80x9cgroupxe2x80x9d does not necessarily signify the assemblage of a plurality of torque transmission paths. For example, it is also possible that every group contains only one individual member, that is, an individual torque transmission path, or is defined thereby. Ultimately, this means that every individual torque transmission path is assigned its own clutch unit and that a plurality of torque transmission paths are not to be serviced by one individual clutch unit. Also, the individual torque transmission paths can be controlled optionally in this way for activation or deactivation of the same. It is also possible, for example, that a plurality of torque transmission paths is contained in one group, while the rest of the torque transmission paths are each positioned individually in respective groups, so that these individual torque transmission paths can again be controlled by their own clutch units and the plurality of torque transmission paths assembled in the group are to be activated or deactivated by a common clutch unit. Basically, the principles of the present invention already result in an improved transmission construction when, in the case of a plurality of groups of torque transmission paths, several of which also comprise a plurality of torque transmission paths, only one individual group is provided in which the torque transmission paths to be activated or deactivated by a clutch unit do not directly follow one another in the defined sequence.
A particularly simple construction can be achieved in that an actuator unit is associated with every clutch unit of the clutch arrangement. The independence of the individual clutch units can be further increased in this way.
For example, every clutch unit for every torque transmission path of the group of torque transmission paths associated with this clutch unit can comprise a synchronizing mechanism.
Further, a particularly simple construction can be achieved in the transmission according to the invention when the transmission has an input shaft and every torque transmission path comprises a transmission member, preferably a transmission gearwheel, which can be coupled by the clutch arrangement to the input shaft for common rotation therewith.
An overly complex construction of the individual clutch units can be avoided when every group of torque transmission paths comprises two torque transmission paths.
The different torque transmission paths can be divided into different groups in a particularly expedient manner in that between every two torque transmission paths of at least one group of torque transmission paths, which two torque transmission paths follow one another in sequence with respect to their transmission characteristic, there is located at least one torque transmission path of another group of torque transmission paths. It will be seen from this that, within the meaning of the present invention, torque transmission paths which are contained in a group of torque transmission paths and which follow one another in sequence are those torque transmission paths between which no other torque transmission paths are located in this group with respect to the sequence. However, due to the fact that no torque transmission paths following one another directly in sequence may be contained in one group, the sequence still has, between two torque transmission paths which are contained in one group and which follow one another with respect to the sequence, at least one additional torque transmission path not contained in this group. For example, if the torque transmission paths for the first gear, the third gear and the fifth gear are contained in a group, the torque transmission path for the third gear is a torque transmission path which follows, but does not directly follow, the torque transmission path of the first gear in terms of the sequence. The torque transmission path which directly follows the torque transmission path for the first gear would be the torque transmission path for the second gear.
It may be provided, for example, that a first group of torque transmission paths comprises the torque transmission paths for a first gear speed and a third gear speed and that a second group of torque transmission paths comprises the torque transmission paths for a second gear speed and a fourth gear speed and, possibly, for a reverse gear.
In a particularly preferred constructional type, it is provided that between two torque transmission paths of at least one group of torque transmission paths, which two torque transmission paths follow one another in sequence with respect to their characteristic, there are at least two torque transmission paths which are not contained in this group. This type of construction of the transmission according to the invention takes into account the fact that in certain driving situations the torque transmission paths which follow one another directly in the sequence are not traversed consecutively but, rather, e.g., at least one torque transmission path occurring in the sequence is skipped. For example, it may happen that when a passing process is started proceeding from fourth gear, the driver may shift back into second gear rather than third gear in order to provide sufficient torque and sufficient engine output. Accordingly, by ensuring that between two torque transmission paths following one another based on the sequence in a group there are two torque transmission paths not contained in this group, it is necessarily ensured that when a torque transmission path is skipped a torque transmission path which is adjusted or active at that moment and a subsequent torque transmission path to be adjusted after skipping over a torque transmission path are not deactivated or activated by the same clutch unit. Therefore, the advantage according to the invention of an appreciably reduced shifting time and appreciably increased shifting convenience is also maintained when skipping over a torque transmission path.
This can be realized, for example, in that a first group of torque transmission paths comprises the torque transmission paths for the first and fourth gear speeds, in that a second group of torque transmission paths comprises the torque transmission paths for the second and fifth gear speeds, and in that a third group of torque transmission paths comprises the torque transmission path for the third gear speed and, optionally, the torque transmission path for a reverse gear and/or a sixth gear speed.
A particularly simple construction of the actuator units can be achieved when at least one of the actuator units has an electric-motor drive unit, preferably a brushless electric motor, which preferably acts on the associated clutch unit via a transmission arrangement.
Particularly when used in commercial vehicles, but also in passenger motor vehicles which generally have a hydraulic or pneumatic circuit, the required shifting force can advantageously be provided in that at least one of the actuator units has a hydraulic or pneumatic cylinder arrangement which acts on the associated clutch unit directly or via a force-converting arrangement, preferably a lever arrangement.
Alternatively, it is also possible that at least one of the actuator units has a lifting magnet arrangement which acts on the associated clutch unit directly or via a force-converting arrangement, preferably a lever arrangement, or in that at least one of the actuator units comprises a piezo actuator arrangement which acts on the associated clutch unit directly or via a force-converting arrangement, preferably a lever arrangement.
As was already mentioned above, the transmission characteristics of the individual torque transmission paths can be defined by a speed reduction ratio provided in the respective torque transmission paths and the sequence of torque transmission paths can be defined by a series of torque transmission paths with ascending and descending speed reduction ratios.
It is noted that within the meaning of the present Application, the xe2x80x9cactivationxe2x80x9d of a torque transmission path means that a determined torque transmission path is changed from a state in which it was not used for transmitting torque between a transmission input shaft and a transmission output shaft into a state in which the force-coupling between the input shaft and the output shaft is achieved by means of precisely this torque transmission path. Accordingly, in this sense, the term xe2x80x9cactivationxe2x80x9d designates the engagement or adjustment of a determined torque transmission path, generally of a determined gear speed.
As was already mentioned in the beginning, different gears are generally selected in conventional shift transmissions in such a way that an actuating element is displaced for selecting a determined shift path and, when the determined shift path is selected, a shifting claw or shifting fork can be moved in one of two directions by rotating the actuating element, so that one of two torque transmission paths to be activated by this shifting claw is activated. When changing gears, the shifting claw must first be moved back again into the neutral position and, if necessary, the actuating element is displaced linearly again and a different shifting claw is moved out of its neutral position into a position activating a torque transmission path. The movement of the actuating element is carried out via a plurality of actuators as is known from EP 0 422 278 A1. In order to overcome the disadvantage of known transmissions of this type, namely, the disadvantage that the time required for carrying out determined shift processes can be relatively long, the present invention further suggests an automatic transmission, especially for a motor vehicle, comprising a plurality of clutch units, wherein at least one torque transmission path of the transmission can be activated by each of the clutch units. According to the invention, an actuator unit is associated with at least one clutch unit, preferably with every clutch unit.
This means that this at least one clutch unit can be controlled solely by the actuator unit assigned to it, i.e., independent from other clutch units. As a result, the sequential movement states required in the prior art for carrying out shifting process can be avoided, since the at least one clutch unit can be activated and deactivated while another clutch unit can be acted on simultaneously or with time staggering.
For this purpose, every actuator unit comprises a drive unit and a driving force transmission unit by means of which the driving force of the drive unit can be transmitted to the respective associated clutch unit.
In order to be able to operate in a construction of the type mentioned above with transmissions of conventional construction, i.e., so that essentially only the conventional mainshaft needs to be replaced by other components, it is suggested that every driving-force transmission unit comprises a transmission shaft which can be set in rotation by the associated drive unit. It is preferably provided that at least two of the transmission shafts of different actuator units are arranged coaxial to one another. It is most preferable that all transmission shafts of the different actuator units are arranged coaxial to one another.
The clutch units can also be accessed directly or a plurality of shifting shafts can be used.
In order to provide sufficient space for positioning actuator units in a simple manner, it is suggested that the shafts which are arranged coaxial to one another penetrate a housing of the transmission and are rotatably supported at the latter. In this case, it is preferably provided that each of the transmission shafts is constructed in a first end area for driving-coupling with the associated drive unit and has, in a second end area, a transmission member by means of which the driving force is conducted to an actuating member of the associated clutch device.
According to an alternative construction, every driving-force transmission unit can comprise a swivelable transmission lever element which is drive-coupled in a first end area with the drive unit associated with the latter and is constructed in a second end area for transmitting driving force to an actuating member of the associated clutch unit.
It is noted that the above-described construction of the driving-force transmission units can be combined with this type of construction in such a way that the driving-force transmission unit which is constructed in the manner of a lever is used for at least one clutch unit and the driving-force transmission unit which is constructed in the manner of a shaft is used for at least one clutch unit.
However, it is preferably provided for this purpose that a plurality, preferably all, of the swivelable transmission lever elements are swivelable about the same swiveling axis.
When a shifting process is carried out, the force required for engaging or disengaging a determined gear speed, i.e., for activating or deactivating a determined torque transmission path, is not constant over the actuating path. Accordingly, only a relatively slight force need be applied at first when disengaging a gear speed until the neutral position of a clutch unit is reached and, when changing to the new gear speed to be engaged, a relatively large force is required in the area of the synchronizing mechanism. Therefore, in conventional transmissions, the actuator units which are used must be dimensioned in such a way that they are capable of delivering or applying the maximum required force, i.e., the maximum required torque. However, this means that the actuating path which can be covered per unit of time is relatively small, which in turn results in that the time required for carrying out a shifting process is relatively long. Therefore, according to another feature of the present invention, it is suggested that a transmission arrangement with variable force transmission and path transmission capability is provided in the force transmission path between a drive unit of an actuator unit associated with a clutch unit and the clutch unit.
By means of transmission arrangements of this kind, it is possible to adapt in such a way that when larger forces must be delivered these forces are also generated, whereas when smaller forces are sufficient, only smaller forces, and hence a greater travel, is generated.
For example, the transmission arrangement can be constructed such that a smaller actuating force or a larger actuating path is provided for the clutch unit in the area of a driving position corresponding to a neutral position of the associated clutch unit than is provided in the area of a driving position of the actuator arrangement which corresponds to a position activating a torque transmission path and/or to a synchronizing position of the clutch unit.
In a particularly simple construction of this embodiment form, the transmission arrangement comprises a noncircular gearwheel arrangement.
In an automatic transmission in which different clutch units are to be controlled by different actuator units, there is basically no mechanical interaction between the clutch units or actuator units themselves. In case of faulty controlling, for example, which may possibly be caused by an error in a control program, this means that when a torque transmission path is already activated by a clutch unit, a different torque transmission path should be activated by a different clutch unit. However, this can lead to a defect in the transmission. In order to avoid such states, it is suggested that a safety arrangement is provided, wherein, when a torque transmission path is activated by a clutch unit, this safety arrangement prevents activation of another torque transmission path by another clutch unit.
For example, it can be provided that the safety arrangement comprises a safety member for at least one clutch unit which, when a torque transmission path is activated by one clutch unit, prevents the actuation of at least one other clutch unit.
The safety member associated with a clutch unit can have at least one activation portion which can be acted upon when the clutch unit is actuated by an actuating portion associated with that clutch unit and has, for at least one other clutch unit, at least one blocking portion which blocks an actuation portion associated with the at least one other clutch unit when the at least one activation portion is acted upon.
However, each clutch unit is preferably provided with a safety member which has at least one activation portion for this clutch unit and at least one blocking portion for all other clutch units.
Particularly in the above-described embodiment form of the actuator units with transmission shafts arranged coaxial to one another, it is preferably provided that the transmission shafts of different actuator units, which transmission shafts are arranged coaxial to one another, are enclosed by safety sleeves which are arranged coaxial to one another, wherein a safety sleeve is associated with every transmission shaft and forms a safety member for the clutch unit connected with the transmission shaft, and wherein every safety sleeve has at least one activation portion cooperating with the associated transmission shaft or with a component connected therewith, and has at least one blocking portion for at least one, preferably all, other transmission shafts or components connected therewith.
For this purpose, every safety sleeve can be displaced in the longitudinal direction of the transmission shafts and pretensioned in a position in which no blocking portion is active and when an activation portion is acted upon each of these safety sleeves can be moved into a position in which every blocking portion thereof blocks any movement of the associated transmission shaft or the component connected therewith.
The present invention is described in detail in the following with reference to the accompanying drawings showing preferred embodiment forms.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.